If you choose to not renew your author license after the 1st year, all your clients going forward will not be able to activate Brizy PRO and benefit of all the features the PRO offers.
(They can however purchase a license directly from us and activate Brizy PRO that way in your theme with no problem if they want to.)
All the clients that already activated a Brizy PRO license in the time your author license was still active will not encounter any issues they will still continue to get updates.
Keep in mind that the licenses that your clients activate are lifetime licenses for them so no matter if you choose not to renew your author license with us, they will not be affected. Only new clients will be affected.